The spent lye, i.e. the so-called black liquor created in pulp manufacture is burnt in a recovery boiler, on one hand, in order to recover the energy it includes, and on the other hand, in order to recover the chemicals in it and to recycle them back to circulation. A char bed is created on the bottom of the recovery boiler when burning black liquor, which in a high temperature forms into smelt, which is removed from the boiler as a continuous flow via smelt spouts to a dissolving tank.
Below the furnace is located the cover area of the dissolving tank of the recovery boiler, i.e. the smelt spout area, where the smelt from the lower part of the furnace is directed along the so-called smelt spout to the dissolving tank. FIG. 1 shows a typical smelt spout area of a recovery boiler, which comprises smelt spouts 2, along which the smelt is directed from the furnace 3 to the dissolving tank 4.
It is necessary to work in the vicinity of the smelt spouts relatively often, because the operation of the smelt spouts must be monitored at regular intervals. When necessary, pluggings must be removed from the smelt spouts in order for the smelt to be able to travel to the dissolving tank. In addition, the primary air nozzles 5 are often located in the vicinity of the smelt spout area (on the so-called primary register level), in which case checking and adjusting the nozzles requires working in the smelt spout area.
Typically, the smelt is very hot (for example 750 to 820° C.). The possible splashes of smelt cause danger to the personnel working and moving in the vicinity. Because of this, there is typically a protection area near the smelt spouts, moving on which area should be avoided and working on which area requires using special protection equipment.